Re: [PATCH 3/3] xen/public: arch-arm: All PSR_* defines should be unsigned

[Juergen Gross <jgross@xxxxxxxx>]

On 18.08.23 10:05, Julien Grall wrote:
> Hi,
>
> On 18/08/2023 09:00, Juergen Gross wrote:
> > On 18.08.23 09:39, Julien Grall wrote:
> > > Hi Jan,
> > >
> > > On 18/08/2023 07:33, Jan Beulich wrote:
> > > > On 17.08.2023 23:43, Julien Grall wrote:
> > > > > --- a/xen/include/public/arch-arm.h
> > > > > +++ b/xen/include/public/arch-arm.h
> > > > > @@ -339,36 +339,36 @@ typedef uint64_t xen_callback_t;
> > > > >   /* PSR bits (CPSR, SPSR) */
> > > > > -#define PSR_THUMB       (1<<5)        /* Thumb Mode enable */
> > > > > -#define PSR_FIQ_MASK    (1<<6)        /* Fast Interrupt mask */
> > > > > -#define PSR_IRQ_MASK    (1<<7)        /* Interrupt mask */
> > > > > -#define PSR_ABT_MASK    (1<<8)        /* Asynchronous Abort mask */
> > > > > -#define PSR_BIG_ENDIAN  (1<<9)        /* arm32: Big Endian Mode */
> > > > > -#define PSR_DBG_MASK    (1<<9)        /* arm64: Debug Exception mask */
> > > > > -#define PSR_IT_MASK     (0x0600fc00)  /* Thumb If-Then Mask */
> > > > > -#define PSR_JAZELLE     (1<<24)       /* Jazelle Mode */
> > > > > -#define PSR_Z           (1<<30)       /* Zero condition flag */
> > > > > +#define PSR_THUMB       (1U <<5)      /* Thumb Mode enable */
> > > > > +#define PSR_FIQ_MASK    (1U <<6)      /* Fast Interrupt mask */
> > > > > +#define PSR_IRQ_MASK    (1U <<7)      /* Interrupt mask */
> > > > > +#define PSR_ABT_MASK    (1U <<8)      /* Asynchronous Abort mask */
> > > > Nit: Did you mean to insert blanks also on the rhs of the <<, like you ...
> > > >
> > > > > +#define PSR_BIG_ENDIAN  (1U << 9)     /* arm32: Big Endian Mode */
> > > > > +#define PSR_DBG_MASK    (1U << 9)     /* arm64: Debug Exception mask */
> > > > > +#define PSR_IT_MASK     (0x0600fc00U) /* Thumb If-Then Mask */
> > > > > +#define PSR_JAZELLE     (1U << 24)    /* Jazelle Mode */
> > > > > +#define PSR_Z           (1U << 30)    /* Zero condition flag */
> > > > ... did everywhere here?
> > > Yes I did. I will update the patch.
> > >
> > > > As an aside I wonder why they're here: They look like definitions of
> > > > processor registers, which aren't under our (Xen's) control.
> > > I agree they are not under Xen's control. However, they are used by the 
> > > toolstack and IIRC back then they were not available in any other headers.
> > > Note that they are only available by the tools and the hypervisor (see #ifdef 
> > > above).
> > > > I ask in
> > > > part because the presence of such constants may then be taken as
> > > > justification to add similar things in new ports. Yet such definitions
> > > > shouldn't be put here.
> > >  From my understanding we are using the public headers to provide 
> > > macros/defines that are used by both the toolstack and the hypervisor. If 
> > > they are not meant to be exposed to the guest, then they will be protected 
> > > with "#if defined(__XEN__) || defined(__XEN_TOOLS__)".
> > > I think we are in a similar situation here. So it is not clear where they 
> > > should be put if we need to share them between the hypervisor and the toolstack.
> > What about include/xen/lib? There are headers below that linked at build time
> > via tools/include/Makefile to tools/include/xen/lib.
> To me, the question is why would we want to move PSR_* in xen/lib (or whatever 
> name we decide) but all the other defines that are only used by the toolstack 
> would still be in public/.
> So are you suggesting to move all the tools only information in xen/lib?
I didn't want to suggest that, especially with our general desire to switch the
tools' interfaces to stable ones.

I just wanted to point out that there are other locations available already
where such information could be shared between hypervisor and tools. Especially
information related to hardware (so not an interface we are defining) might be
a good candidate for such an alternative location.

But in the end it is not me to decide what to use. I was just giving a hint. :-)


Juergen

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